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13th May 2008, 4:58 pm | #1 |
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Bush TV12A/B alignment problems
Hi all.
A short while ago, I bought a TV12B on ebaY. The type number was on an etched brass label clipped to the cover by means of two tongues fitted into slots in the CRT neck cover. However, the label over the aerial socket said "LONDON"! After a bit of work, I got a picture using my Aurora on CH4, not CH1. The RF chassis fitted is definitely a London version but some of the capacitors in the RF stages had been changes (lower values). I lifted the etched TV12B label and underneath was printed TV11A - the plot thickens. I decided to revert to CH1 by replacing the Cs with appropriate values and re-aligning but I cannot get the set to tune low enough. There are no capacitors in the coupling tuned circuits (it's a TRF) so I suspect that turns have been removed so I opened the first can but cannot see obvious changes although the soldered joints had been disturbed. Can anyone suggest what is going on!! Cheers Brian PS Why is the TV12 fitted with a Belling-Lee aerial socket and the TV22, a later set fitted with terminals? Any ideas. |
13th May 2008, 5:31 pm | #2 |
Dekatron
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Re: Bush TV12A/B alignment problems
This may have been modified in the past, but the TV11 and TV12 are similar.
Manual available here: http://www.thevalvepage.com/download...2.pdf&dir=bush How low does it go? Channel 1 is lower than the rest of course. Make sure all the caps are the ones specified in the diagram and then look at the coils. http://en.wikipedia.org/wiki/LC_circuit If the coils can't be adjusted to fit, try adjusting capacitor values, or fitting caps across the coils? I think someone tried to convert this and made a bit of a mess! Cheers, Steve P.
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13th May 2008, 5:34 pm | #3 |
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Re: Bush TV12A/B alignment problems
I too was a bit surprised to find a co-ax socket on mine, as I was expecting to find terminals there as with the later TV22. A nice surprise though,as it makes life easier. Mine is the Birmingham version, at least it says so on the little disk fitted round the aerial socket
I'll have a proper look later Yours will certainly have had turns removed for it to receive Birmingham Ch4. BG >EDIT< Thanks for the link Steve, I'll need that too |
13th May 2008, 5:56 pm | #4 |
Hexode
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Re: Bush TV12A/B alignment problems
Brian,
I believe that the TV11 and TV12 are electrically the same, the TV11 being the wooden cased version of the TV12. My own TV12 has a Belling-Lee aerial socket too, so this is clearly correct, although one does have to wonder why they used a rather fiddly connector on the later TV22.
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13th May 2008, 8:40 pm | #5 | |
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Re: Bush TV12A/B alignment problems
Quote:
The serial numbers of the chassis are: RF - 68 0230 main: 64 - 00279 which suggest they are both very early in the production run. Could it be that the modification was done by Bush as a stopgap before the redesigned TV12B was available in quantities. The midland service started 17th Dec 1949 and the TV12B was released (or announced) Sept. 1949 so I guess it is a possibility. I have looked more closely at the joints of the coils to the valveholders and the majority look original (colour and quality) except that on desoldering several, I have found that there are signs of a previous coil connection which has been cut, leaving a couple of turns round the tag! I find it all very strange and it's going to be difficult to change! Perhaps I should put it back to as it was regardless of the LONDON label on the aerial socket! Cheers Brian |
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13th May 2008, 8:50 pm | #6 |
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Re: Bush TV12A/B alignment problems
It is not unusual to find original Bush backs with the metal plate covering another model from the range. My TUG24 console is another example. The metal plate says TUG24 and the printed label underneath says TUG12A..The set is original having been obtained from a cutomer that purchased it new. Regards, John.
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24th May 2008, 8:49 pm | #7 |
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Re: Bush TV12A/B alignment problems
I've looked a bit more into this problem! The vision interstage transformers do not peak at the channel 4 frequency but a bit lower than the sound frequency - strange.
I removed a can - not an easy job - to see if the coils had been modified but they looked untouched. However, the adjustable cores are brass not ferrite. This could have been a way to raise the frequency of the London coils without removing turns (there are no capacitors in the tuned circuits, strays being used). Question is are the cores in the normal London chassis ferrite - anyone know? I am still convinced that this set has not been converted/bodged by a punter. It really does look like a works modification and certainly contemporary with the manufacture of the set. Any ideas? Cheers Brian |
27th May 2008, 11:15 am | #8 |
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Re: Bush TV12A/B alignment problems
Hi Brian,
are you sure about the brass cores? I've not looked inside my own TV11A, but Bush products of the time (such as the DAC90 radio (not the 90A)) used a brass rod with a ferrite molded on the end. These ferrites will break off if the rod has been screwed up or down too far. The result being a coil that won't align. Cheers. Andy |
3rd Jun 2008, 12:39 pm | #9 |
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Re: Bush TV12A/B alignment problems
Hi Andy - sorry about the tardy response but I've been away!
I have removed the cores from two of the cans and they both have lumps of brass fitted onto the 4BA threaded rods. When I took the first one out, I expected to see a lump of ferrite on the end of the rod as you suggest and was surprised to find the brass. This is what makes me wonder whether this is a factory "bodge"! I am trying to source some 8mm ferrite which I can use to see if the transformers would then tune down to 45MHz (or do I mean 45Mc/s?). Of course, the standard aerial rods are too big. I will eventually try to get it working on channel 4 but I want to prove whether the coils will tune down far enough. Cheers Brian |
3rd Jun 2008, 8:17 pm | #10 |
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Re: Bush TV12A/B alignment problems
Hi Brian, ferrite can be reduced in diameter by centerless grinding and holes can be added (carefully ) with a carbide drill. I'm not to sure how well an aerial rod would work as it may be a bit lossy at 45MHz, but worth a try.
Ed |
3rd Jun 2008, 11:34 pm | #11 |
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Re: Bush TV12A/B alignment problems
Hi Ed
Unfortunately, I don't have a centreless grinder so I tried glueing a ferrite core with a hexagonal hole to a bit of 4BA studding filed to suit. I did this on L3/L4 in the anode of the first stage and, low & behold, it peaked at 43.5Mc/s - the frequency stated for channel one! Does this suggest that I have an early London Fringe RF chassis (serial no. 230) factory converted to receive the Birmingham TX? The whole point of starting this thread was to try and get some thoughts on the reason for such a modification (although the "London" plate behind the aerial socket was not altered). I found that the cores could be removed without de-soldering the connections to the transformers by releasing the cans, removing the coils and laying them, still connected, over. Why then, had all the coil connections have been made twice (suggested of the first connections having been cut)? Perhaps it was deemed easier to do in the factory rather than the fiddly job of removing the coils from the cans while still connected. I know this is a bit esoteric but I found it very strange to get a TV with a Birmingham label added in the factory with a London RF chassis but tuned to CH 4. In the TV12 RF chassis, the Birmingham version has 4 extra tuned circuits for sound rejection and bandwidth limiting - does this suggest that this is a requirement because inductors with brass cores have a lower Q? It must make the manufacturing costs a lot higher. Cheers Brian |
4th Jun 2008, 12:46 am | #12 |
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Re: Bush TV12A/B alignment problems
Well, Sutton Coldfield opened in December 1949. I wonder if this was a set that was factory modified for test transmission monitoring before the Bush factory geared up for Ch4 set production proper?
You might have an important set there. |
4th Jun 2008, 3:08 am | #13 | |
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Re: Bush TV12A/B alignment problems
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4th Jun 2008, 1:02 pm | #14 | |
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Re: Bush TV12A/B alignment problems
Quote:
Cheers Brian |
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5th Jun 2008, 2:28 pm | #15 |
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Re: Bush TV12A/B alignment problems
Brianc,
the TV11a definately was fitted with a Belling Lee style aerial socket and the coils on the R.F. chassis were fitted with iron dust cores glued to 4BA brass studding and slotted for screwdriver adjustment. Ferrite was not available in 1949 at least not for R.F. Our family purchased one in 1949, it was the London chassis, it set gave magnificant pictures and was fitted with an MW22/14C tube. The set remained in with our family for about twenty years and was still operating when it was disposed of, strangely I don't recall seeing an ion burn even when it was twenty years old. Victor. Last edited by ENGLISH VICTOR; 5th Jun 2008 at 2:39 pm. |
5th Jun 2008, 8:37 pm | #16 |
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Re: Bush TV12A/B alignment problems
Thanks Victor, you're right, I should have said "iron dust" instead of Ferrite!
However, your statement does seem to prove that the cores in my set have been changed to brass to raise the tuning to Channel 4 but it still has a London label over the Belling-Lee socket. One would have thought that if the coil cans were removed to change the cores (it is physically necessary to do so), the London label would have been changed - it is fitted with screws, not pop rivets. I wonder how many more sets of this type are out there?? Cheers Brian |
5th Jun 2008, 10:27 pm | #17 | ||
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Re: Bush TV12A/B alignment problems
G8KBG:
Quote:
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So what you might just have here is one of the few sets that fell into the dealer's hands before the service started. Intriguing thought, isn't it. And it's probably unreasonable to expect that Bush got it completely right when they modified a Ch.1 chassis, so some of the oddities that you see may be field-modifications issued by the manufacturers and carried out by the dealers - I can imagine the blurry roneo'd typewritten mod-sheets even at this distance in time. What fun, eh. |
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